Here are a few things to help you prepare for the AMC exams
The Mathematical Association of America has been running the American Math Competition for a long, long time. Over 300,000 students nationwide participate in their contests every year. Here is the AMC web site with tons of general information about the AMC contests and more
Jabe Blumenthal, legendary Lakeside math teacher of yore, wrote up a document that collects just about every mathematical fact you would ever need to know to get a perfect score on the AMC contests. A scanned version of that document is right here.
And finally, the Art of Problem Solving has the ultimate archive of past contests. Here are their AMC 10s, and their AMC 12s. Almost all of the problems come with solutions, which you can find by clicking the “view topic” link on the right.
This year Lakeside will be giving the AMC 10A and 12A on Wenesday, February 7, 2018, from 8:10 am to 10:00 am. If you haven’t signed up yet, and you’d like to participate, just send an email to “dean <dot> ballard <at> lakesideschool <dot> org”.